In a mixing bowl, whisk together the all-purpose flour and salt until combined. Cut in the unsalted butter until the mixture resembles coarse crumbs. Gradually add ice cold water until the dough holds together. Shape into a disc, wrap in plastic, and chill in the fridge for 30 minutes.

Preheat your oven to 425°F (220°C). Slice the butternut squash into small cubes, drizzle with olive oil, and sprinkle with spices. Toss to coat, spread on a baking sheet, and roast for 15-20 minutes until tender.

Heat olive oil in a skillet over medium heat. Add sliced red onion and sauté for 3-5 minutes until translucent. Remove from heat.

Reduce oven temperature to 350°F (175°C). Roll out chilled dough on a floured surface into a circle. Transfer to a parchment-lined baking sheet, spread Boursin cheese, and layer roasted squash and sautéed onions.

Fold the dough edges over filling, brushing crust with heavy cream and sprinkling with Parmesan cheese.

Bake for 45-50 minutes until golden brown and filling is bubbling. Cool for 10 minutes before slicing.